(a) The board of trustees shall designate an actuary who shall be the technical advisor of the board of trustees on matters regarding the operation of the funds created by this chapter and who shall perform such duties as are required in connection therewith.

(b) From time to time, but at least once in every five-year period, the actuary shall make an actuarial investigation into the mortality, service, and compensation experience of the members and beneficiaries of the retirement system and recommend for adoption by the board of trustees, mortality, service, and other tables needed in the operation of the retirement system. Taking into account the results of such investigations, the board of trustees from time to time shall adopt for the retirement system such mortality, service, and other tables as it shall deem necessary for use in all calculations required in connection with this retirement system. The board of trustees shall also determine from time to time the rates of regular interest for use in all calculations required in connection with the retirement system, limited to a minimum of 2 percent.

(c) On the basis of regular interest and the tables last adopted by the board of trustees, the actuary shall make annual valuations of the contingent assets and liabilities of the retirement system.